A pulse Doppler device transmits/receives waves such as pulse ultrasonic waves or electromagnetic waves to/from an object and analyzes time-series signals obtained by arranging signals of a particular point of time with equal lapse time from pulse transmission times of a plurality of received echo signals as shown in FIG. 1 in order of the transmission times, thereby obtaining information such as velocity of a moving object. The most common signal processing method performs quadrature detection on the reception signals and analyzes them as complex time-series signals. Such a pulse Doppler device is widely used as an ultrasonographic device for detecting and drawing a blood flow or the like in a living body, a meteorological radar for detecting and drawing rain clouds, an airborne radar for detecting a flying object, or the like.
If only one reflector exists, a motion velocity “v” of the reflector approaching or moving away from a transmitter/receiver can be easily obtained as follows using a phase rotation velocity λΔΦ/Δt of the time-series signals, that is, a signed angular frequency.v=λΔΦ/Δt/2π  (1)
where λ denotes wavelength, Δt denotes time interval of pulse transmissions, and ΔΦ denotes a phase rotation angle. In the case where the reflector approaches, the sign “v” is positive. In the case where the reflector moves away, the sign “v” is negative.
In a reception echo of an actual pulse Doppler device as described above, however, the strength of an echo signal from a stationary reflector or so-called clutter signal is generally higher than that of an echo signal from a target moving reflector by a few digits. Consequently, only by simply applying the process of the equation (1) to the time-series signals, a moving reflector cannot be detected. An actual pulse Doppler device is therefore constructed to suppress an echo signal from a stationary reflector, perform a signal process called an MTI (Moving Target Indicator) process of relatively emphasizing an echo signal from a moving reflector and, after that, detect or analyze velocity.
In “IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control”, Vol. 42, pp 927-937, 1995, a polynomial regression filter is proposed. The polynomial regression filter is a process of sequentially least-square fitting expressions of the 0th order (constant), the 1st order, the 2nd order, . . . , and the Mth order to the time-series signals and eliminating fit components, thereby eliminating drift components of the original time-series signals.